This invention relates to electric arc-welding processes and apparatus therefor, and more particularly to inert gas-shielded arc-welding processes and apparatus.
In inert gas-shielded arc-welding, a weldpool is produced in a welding zone on the workpiece by the heating effect produced by an electric arc struck between a welding electrode in a holder and the workpiece. The weld pool is shielded from contamination by the blanketing effect of an inert gas, such as helium or argon. Either direct current or alternating current may be used to provide the welding current depending to a large extent on the nature of the material to be welded.
Direct current welding is usually carried out with the welding electrode negative, less heat being generated in the electrode than in the positive workpiece. When welding with the welding electrode positive, more heat is generated in the electrode but a "scouring" action is produced on the surface of the workpiece, which makes it possible to weld materials such as aluminium which readily acquire a oxide film.
Welding with conventional alternating current derived, for example, through a transformer from a mains 50 or 60 cycles per second supply, or an engine driven alternator, combines in one cycle, or repetition period, a negative pulse of current for one half-cycle and a positive pulse of current for the other half-cycle. Alternating current is therefore usually used for welding materials such as aluminium by the gas-shield arc-welding process since it combines the features of both electrode positive and electrode negative welding.